Ion getter pump



Aug. 9, 1960 M. VON ARDENNE 2,943,459

ION (mm-1 PUMP Filed July 22L, 1958 g H x a g 19 6 I; x 1s 17 6 L L *aaoy 800V INVENTOR United States Pat n ION GE'ITER PUMP Manfred von Ardenne, Dresden-Weisser Hirsch, Germany, assignor to VEB Vakutronik DresdemDresden, Germany Filed July 22, 1958, Ser. N0. 150,255 Claims priority, application Germany 12, 1957 4 Claims. Cl. 230-69 The evaporators used for dispersing the getter metal are usually heated by electron bombardment to the high temperatures required. As a consequence, such a pump will start operating or, if Started, will maintain stable operation only if the pressure of residual gas is first reduced to 10- mm. Hg or less.

According to another known type of ion getter pump design, the evaporator is heated by gas discharge which changes to a vapor discharge in the vapor of the getter metal as soon as evaporation of the getter material is initiated. This device requires the getter metal to be evaporated continuously without interruption in order to prevent a break in the discharge. As a result, the consumption of getter metal is higher by one or two orders of magnitude than would be necessary for merely producing the getter pump effect.

The apparatus required for the two types of ion getter pumps described above and for their modifications that have become known so far is rather complicated and its operation is difficult.

An object of the present invention is the provision of an ion getter pump which is simple is design and, therefore, is relatively low in first cost of construction.

Another object is the provision of a pump which is economical in its operation and of high efficiency.

A further object of the invention is to generally improve ion getter pumps as presently known and to overcome the disadvantages thereof. 7

Other objects and manyof the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing in which the single figure shows a vertical section of an embodiment of the ion getter pump of the invention.

Referring now to the drawing, there is shown a pump chamber formed by a cylindrical body 1 having a bottom 2 joined thereto by a flange connection. A tight seal is formed between the cylindrical wall 1 and the bottom 2 by a metallic gasket 30. The cover 22 is formed with openings 21 which communicate with the container which is to be evacuated. The container may be directly attached to the pump cover 22 without any intermediate refrigerated cold traps. A tubular duct 3 connects the pump chamber with a roughing pump capable of producing a vacuum of approximately 10" mm. A rotating mechanical pump such as a Roots pump is suitable.

An integral evaporator-cathode is arranged axially in the lower part of the pump chamber. It consists of an upright hollow cylindrical structure 4 of refractory conducting material such as tungsten sheet closed at its upper end by a circular disc 5 of the same material and slotted 2,948,459 Patented Aug. 9, 1960 in an axial plane almost over the entire length of the cylinder. The cylinder 4 is mounted on two lead-in conductors 31 tightly sealed into the bottom plate 2 of the pump chamber and connected to a source of electric potential for current flow through the evaporator-cathode. The length of the slot 4a is selected in such a manner that the evaporator disc 5 will reach approximately the same temperature as the cylindrical cathode body 4 when the latter is heated to theemission of electrons by passage of electric currents A funnel 9 is elastically suspended from the top cover 22 of the pump chamber in electromagnet 6 actuating. avibrator 7 with a clapper 8 attached thereto is arranged for vibrating the funnel 9 when energized by alternating current supplied through conductor 23. Funnel 9 holds granular getter material 10 such as titanium powder of relatively uniform grain size. The apex of funnel 9 is perforated to form an opening 29. The size of the opening 29 and the inclination of the funnel walls is such that the getter material will not pass through the opening unless the funnel is shaken by the clapper 8. The granular material released through the opening 29 passes through a tubular element 11 which confines the stream of particles to a narrow path. On their downward movement, the particles of getter material strike a baffie arrangement 12 which breaks the velocity of their fall sothat they impinge on the evaporator disc 5 at relatively low speed.

The'inner surface of the cylindrical body 1 is provided with a removable metallic liner 13 for receiving the dispersed getter material which can then be reclaimed therefrom. Liner 13 is in electrical contact with cylinder 1.

A grid-like electrode 14 which may consist of a loose network of fine tungsten wires is arranged between the evaporator disc 5 and the tubular element 11. The electrode 14 has the shape of a cylindrical drum coaxial with the pump chamber. It has an axial opening at the top for passage of getter material and is equipped at its lower end with a tubular extension 15 which surrounds the, cylinder 4 at a radial distance of a few millimeters.

A conical sheet-metal reflector electrode 16 is mounted axially below the grid 14 and envelops the extension 15 of grid 14. A magnetic field is formed within the grid 14 by two permanent magnets 19' and 2 0 fastened to the top cover 22 and the bottom 2 of the pump chamber. The magnets are equipped with pole pieces 17 and 18, respectively. The magnetic circuit of magnets 19 and 20 is closed by the bodyof the pump.

The operation of the illustrated pump will now be described separately as to its getter pump effect and to its ion pump effect. The getter pump action will be described first.

The pump chamber is evacuated to approximately 10-' mm. by means of the roughing pump connected to duct 3, and alternating current is passed through the cylinder 4 and disc 5 to heat them to a temperature of 2,000 C. to 2,500 C. This temperature is higher than would actually be required for evaporation of pure titanium metal since the vapor pressure of titanium is sufficiently high at 1,600 C. to 1,700 C. to achieve the desired getter effect. Titanium surfaces, however, and particularly the surfaces of titanium powder particles-such as are supplied tothe evaporator surface in thepump of the invention are coated with an oxide layer which must be fused and evaporated requiring temperatures which were determined by experiment to be above 2,000 O. This is precisely the temperature at which such refractive metals as tungsten or tantalum emit electrons at a good current density (order of magnitude of I ampere per square centimeter). {The pump of the invention makes use of the similarity of the temperature required for the getter metal and for electron emission by the thermionic an axial position. A small 7 cathode for providing a particularly simple and efficient arrangement.

When the vacuum has reached the required value and the evaporator disc 7 the electromagnet 6 is energized by alternating current provided, for example, from lighting mains via control means such as a variable resistor or transformer. By controlling the force with which the clapper 8 vibrates the funnel 9, the rate of release of the titanium powder from the opening 29 may be varied. The stream of titanium particles is concentrated into a narrow beam by the tubular element 11 and the fall of the particles is broken by the bafile arrangement 12. It has been found that a major portion of metallic particles dropped upon the evaporator disc from a height of only a'few centimeters rebound without evaporating and are scattered in the area surrounding the evaporator. The baffle 12 effectively prevents such loss of getter metal. The titanium particles are evaporated substantially instantaneously upon contact with the disc 5 and metal' losses are practically eliminated. The getter material is condensed on the inner surfaces of the pump chamber and particularly in the central portion of the cylindrical body 1 covered by the liner 13.

Contrary to a diffusion pump, the getter pump becomes operative as soon as it is started. The roughing pump is to be disconnected shortly after starting. A valve or other known means may be provided for the this purpose. In order to reduce the vacuum as rapidly as possible from the level obtained by the roughing pump to the high vacuum of which the pump of. the invention is capable, it is preferred to supply getter material continuously during the starting-up period for continuous gettering. The relatively large amount of gas present initially is thus cleaned up both by dispersal gettering in the free space of, the pumping chamber and by contact gettering at the deposited metal. layer. As soon as the initial stage is passed, contact gettering alone is sufiicient for completely evacuating the container communicating with openings 21. Getter material is, therefore, supplied either intermittently or continuously in greatly reduced amounts. The pump may be set for such reduced gettering by eitherarranging a time-switch in the energizing circuit of magnet 6 or by reducing the exciting current r h ma net- The use of granular getter material such as powder is preferred because of, the ready availability and the relatively lovy costof powdered titanium, butitis apparent that a wire shaped getter metal may be fed to the evaporator disc by a suitable mechanism. vious to those skilled in the artthat other metals may be substituted for titanium without departing from the spirit of the invention although titanium is preferred because of its great chemical activity, the low vapor pressure of the metal and of its Compounds formed in the pump, and the fact that such titanium compounds are stable solids at room temperature.

'The operation of the pump of the invention as an ion pump will now be described. This separate description is not to imply, though, that the two functions are separate and independent. It will be readily understood-that the two modes of operation of the pump of the invention are intimately interconnected and that this connection and combination ofthe two functions is an important feature of the invention.

ing in aslong a path as possible. The resulting ions of residual gas are accelerated to several-hundred'volts in the pumping field and are driven into the active surface of the getter deposit. When rare gases are to be evacuated, the accelerating potential is preferably ofthe order ofmagnitllde of 800 for drawing off electronsfrom the cathode at high Car- 5 is at the necessary temperature,

It will also be obvolts, This voltage is also suitable rent density with the usual spacing of the cathode from the collector electrode without critical limitations by space charges. With proper dimensioning of the electrodes and suitable spacing the same source of potential may be connected to the grid-like electrode 14 and to its extension 15 for drawing off the electrons from the cathode cylinder 4 and for accelerating. the. ions of the residual gas from the ionization space toward the layer of getter condensate, The getter ion pump of the inventionthus requires but three sources of current, namely:

-'(l) Direct current at somewhat below 1,000 volts for simultaneous drawing-oi of electrons and acceleration of the ons. produ e (2) Alternating filament current for evaporator-cathode, and

(3) Alternating current for tuating magnet.

The active surface of the cathode is the surface of cylinder 4 which by. its vertical disposition is protected om contact with and contamination by the getter material which would otherwise reduce the emissivity or alter the characteristics of thethermionic emission by formation of alloys. The disc 5 which serves as an evaporator does not or does not substantially contribute to electron emission.

' The use of an axial magnetic field produced by m agnets 19 and 20 and heating by means of alternating current limits the electrodynamic forces acting on cathode 4, thus reducing or practically eliminating deformation and premature failure by vibration.

The special configuration of the evaporator-cathode of the invention permits reaching the necessary temperature of 2,000 to 2,500 resorting to the complicated method of electron bombardment. The useful life of the evaporator-cathode is long and its efliciency is maintained over extended periods.

operation of the energizing the clapper-ac- The single grid-like electrode 14 draws the electrons.

from the cathode and defines the ionization space proper.

The extension 15 which constitutes a pumping grid would;

draw off; electrons from cathode 4 in a substantially radial direction thus causing the electrons, to move. in. undesir- Preferred paths of electrons are confined:

able paths. within the field-free ionization space, and are of maximum length. The invention, therefore, provides a refiectorsheet 16 which is brought substantially to thevoltageof the cathode and which reflects the stream. of electrons into the ionization. space enclosed by gridexten sion 15 The. auxiliary magnetic field produced bymagnets 1 7 and18.forces the electrons into helical paths thus greatly increasing the length. thereof.

The paths of by application of an oscillating electric field of high frequency, whereby the electrons would be forcedto oscillate. at high frequency. This method of increasing the length of path of theelectrons is entirely within the scope of the present. invention. The arrangement illustrated, however, is preferred because. of the lower cost of the apparatus required.

The auxiliary magnetic field extends between the pole pieces 17 and 18 excited by permanent magnets 19 and 20 which may be arranged within the evacuated space as shown or may pump chamber proper.

With a distance of a few millimeters between cathode 4. and pumping gridextension 15- and with a potential of approximately 800 volts, a current density of approximately one ampere per squarecentimeter can be obtained C. very conveniently and without.-

the electrons. could also be lengthened be arranged outside of the evacuated in the drawingis of the order of 1 cm. sothat the system illustrated provides. an electronjstream of approximately one ampere for. ionization alongthe specially extended paths of' the electrons. The

ions generated in the ionization space pass through the openings in grid 1-4 into a field which accelerates the ions towards the interior wall of the pump body 1 and drives them into the active getter layer on liner 13.

It the highest possible vacuum is to be produced with the apparatus of the invention the metal parts of the internal elements as well as the pump housing have to be cooled and special seals of materials which have very low vapor pressure must be employed as is well known. When these necessary precautions are taken, the pump of the invention rapidly reaches vacua of to 10 mm. Hg even in rare gases, and also in the common gases such as hydrogen, nitrogen, oxygen, and the like.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. An ion getter pump for producing -a vacuum by means of the evaporation of a getter material and the ionization of the residual gas in an ionization space by electrons emitted by a cathode, comprising a housing having an opening for communicating with a container to be evacuated, an integral evaporator-cathode of refractory conducting material mounted in said housing and having a cathode portion and an evaporator portion distinct from said cathode portion, 7 means connected to said evaporator-cathode for passing electric heating current therethrough, means adjacent the evaporator-cathode for supplying getter material to the evaporator portion of said evaporator-cathode, and means in said housing spaced from the evaporator-cathode for collecting the evaporated getter material and the ions of the residual gas in said housing.

2. An ion getter pump as set forth in claim 1, further comprising first electrode means spacedly arranged adjacent the cathode portion of said evaporator-cathode, and second electrode means defining an ionization space accessible to electrons emitted 'by said evaporator-cathode, and a source of positive potential connected to said first and said second electrode means, whereby electrons are drawn off the cathode portion of said evaporatorcathode and ions formed in said ionization space are accelerated.

3. An ion getter pump as set forth in claim 2, further comprising deflector electrode means arranged intermediate said evaporator-cathode and said second electrode for deflecting ions emitted by said cathode portion, and a direct electrical connection between said deflector electrode means and said evaporator-cathode.

4. An ion getter pump as set forth in claim 1, said evaporator-cathode comprising a hollow cylindrical structure axially slotted over a major portion of the length thereof, said cylindrical structure being closed at one end thereof by a disc integral therewith.

5. An ion getter pump as set forth in claim 1, said refractory conducting material being a refractory metal selected from the group consisting of tungsten and tantalum. v

ranged entirely within said pump above the evaporator portion of said evaporator-cathoda'and electromagnetic means in engagement w th said storage means for selectively releasing said getter material from said storage means.

9. An ion getter pump as set forth in claim 8, further comprising baffle means arranged intermediate said storing means and-said evaporator portion for breaking the fall of said getter material released from said storage means. I

10. In an ion getter pump for producing a vacuum by means of the evaporation of a getter material and the ionization of the residual gas in an ionization space of the pump by electrons emitted by a cathode; the improvement comprising an integral evaporator-cathode of refractoryconducting material having a cathode portion and an evaporator portion distinct from the cathode portion, means connected to said evaporator-cathode for supplying electric heating current thereto, means mounted immediately above said evaporator-cathode for supplying getter material to the evaporator portion only of said evaporator-cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,850,225 Herb Sept. 2, 1958 

